This invention relates to a method of manufacture of light weight, flexible, thin film photovoltaic devices.
A method of flexible photovoltaic device manufacture is described in Japanese public disclosure 85872 (1986). As shown in FIG. 1, the method described in this disclosure has a glass substrate 11 on which a metal layer 12 is formed to serve as a back electrode. On top of the metal layer 12, an amorphous silicon layer 13 and a transparent surface electrode 14 provided with ITO layer and a collector, are formed in that order. The glass substrate is then separated from the photovoltaic device. Metals such as stainless steel, chrome, and silver are used as back electrodes for the metal layer 12. Stainless steel and chrome metal layers 12 have the drawback that they do not separate well from the glass substrate. Because of this, even separation of the glass substrate 11 is difficult and not practical. On the other hand, the glass substrate 11 separates well when the metal layer is silver. However, silver has the drawback that it diffuses into the amorphous silicon layer 13 when it is formed on the silver metal layer 12 and degrades performance as a photovoltaic device.
Japanese public disclosure 105581 (1989) describes a method for eliminating these types of drawbacks. As shown in FIG. 2, the method described in this disclosure has a supporting substrate 21 on which a polyimide resin layer as the first resin layer 22, a transparent electrode layer 23, an amorphous silicon semiconductor layer 24, a backside metal electrode layer 25, and a second resin layer 26 are formed. The supporting substrate 21 is then separated from the first resin layer 22 by immersion in water.
However, because the separation layer is the first resin layer 22 which is a polyimide resin layer, this method has the following drawbacks.
1 Polyimide resin can withstand heat up to a maximum of about 300.degree. C. For this reason, tin oxide (SnO.sub.2) film which has a formation temperature of 600.degree. C. cannot be put on the first resin layer 22. Consequently, tin oxide with low resistivity and high optical transmissivity cannot be used, and some high resistivity conductor must be used in its place. PA0 2 When the multilayered structure is separated from the supporting substrate 21, the separation is uneven and repeatability is poor. PA0 3 Because the first resin layer readily absorbs water, it generates gas within the vacuum chamber during formation of the photoelectric layer. This gas becomes incorporated into the photoelectric layer and degrades film quality.
Further, as shown in FIG. 3, Japanese public disclosure 107073 (1988) describes a method of photoelectric device manufacture with a glass supporting substrate 31 on which a heat resistant transparent resin layer 32, a transparent electrode layer 33, an amorphous silicon layer 34, a metal electrode layer 35, and a protective resin 36 are formed in that order. This multilayered structure is immersed in water causing separation between the glass substrate 31 and the heat resistant resin 32.
Since the method of manufacture described in this public disclosure also attaches synthetic resin onto a glass supporting substrate, it has drawbacks similar to those of the method shown in FIG. 2. Namely, since this method attaches transparent synthetic resin 32 onto the glass supporting substrate 31, it is not simple to grow a high formation temperature tin oxide (SnO.sub.2) film as the transparent electrode layer. It is also not simple to separate the heat resistant transparent resin 32 from the glass supporting substrate 31. Further, during formation of the amorphous silicon layer, out-gassing within the vacuum chamber degrades the film quality of the photovoltaic layer.
The present invention provides a thin film photovoltaic device with exceptional flexibility that can be easily separated from the supporting substrate without immersion of the multilayered structure in water.